Fuel cells are a known way of converting the energy of fuel directly into electrical energy. A typical structure for a fuel cell includes a pair of porous electrodes, i.e. a fuel electrode and an air electrode, with an electrolyte layer therebetween. The fuel electrode is in contact with hydrogen, and the air electrode is in contact with oxygen. A fuel cell with such a structure generates power by electrochemically reacting hydrogen and oxygen.
In a power generation system that uses natural energy, such as photovoltaic power generation or the like, the power generating capability varies depending on the natural environment. As long as fuel and air are supplied, however, a fuel cell can stably provide electrical energy. Therefore, for home power generation during a power outage or the like, a device that uses a fuel cell to support a function for self-sustained operation of power generation while disconnected from the power grid (commercial power supply) is under study (for example, see Patent Literature 1).
Patent Literature 1 proposes a fuel cell system that facilitates an operation to follow a power load of a load device (referred to below simply as a “following operation”). When reforming raw fuel into hydrogen, this fuel cell system uses an exothermic reaction such as a partial oxidation reaction. Therefore, the fuel cell system does not use the exhaust gas from the fuel cell itself as a source of heat for the fuel reforming unit. In response to the power demand and heat demand, this fuel cell system can, within the fuel cell itself, change the amount of raw fuel provided to the fuel reforming unit and the fuel usage rate of the fuel cell itself.
In recent years, research has been conducted on a Home Energy Management System (HEMS) that controls a load device within a home and an energy control system provided with a fuel cell capable of self-sustained operation without receiving power from a power grid (commercial power supply) during a power outage. In such an HEMS, it has been proposed to cause the fuel cell to generate a larger surplus power than the load power consumption within the home in advance and to execute control so as to cause an appropriate load within the home to consume the surplus power. According to such an HEMS, the poor load following capability of the fuel cell can be improved to some degree, and by appropriately consuming the surplus power, a somewhat comfortable environment can be created even during a power outage.
On the other hand, with photovoltaic power generation, the power generating capability varies depending on the natural environment, such as the location of the solar panels, the duration of sunlight, and the like, as described above. Nevertheless, photovoltaic power generation is attracting attention as a technique for generating a substantially inexhaustible supply of power as long as sunlight is available. Furthermore, when a photovoltaic power generation device installed in an average home or the like, for example, produces surplus power while generating power, the surplus power can be sold to the power grid under predetermined conditions.
The power that is thus sold to the power grid can be sold at a relatively high price. Accordingly, by using both fuel cell power generation and photovoltaic power generation, economical operation can be achieved by providing the power generated in the fuel cell to a load device while selling the power generated by photovoltaic power generation to the grid and applying the payment for the sold power to the cost of fuel for the fuel cell.